1. Field of the Invention
This invention relates to the spectral analysis of wood, and in particular to a method for predicting dry mechanical strength properties from the near infrared (VIS-NIR) spectra (350-2,500 nm) of green wood using a multivariate calibrations model, in follow-up to and based upon provisional application serial No. 60/214,380, filed Jun. 28, 2000.
2. Description of the Prior Art
A method for the nondestructive analysis of the quality and value of a tree, unlike conventional methods, which measure the volume and form of a tree, would provide important information to assist woodland owners in making their thinning decisions, and in the valuation of a stand of timber. The method would also be useful in the analysis of trees or sawn logs, in the woods, for the field sorting of logs to be used as poles, or feedstocks in the manufacture of veneers, lumber or chips, or in the early stages of the wood manufacturing operation.
Visible and near infrared (VIS-NIR) spectroscopy (350-2,00 nm) in combination with multivariate data analysis is currently in use for the characterization of complex systems. These several statistical methods are also termed chemometric methods, forming the discipline of chemometrics, when applied generally to the field of chemistry, and in particular to the field of analytical chemistry. The technique of chemometrics is more fully explained in Brown, S. D., AChemometrics@, Anal. Chem. 62, 84R-101R (1990).
Chemometrics has been described for use in the non destructive analysis of the chemical and physical properties of paper.
For example, U.S. Pat. No. 5,638,284 describes a method for the measurement of the wet strength of paper by analyzing the visible, near-infrared and/or infrared spectrum of the paper/pulp in the process line using a wavelength range within 400 nm to 4000 nm, and applying a chemometric evaluation of the spectrum, to calculate the wet strength of the paper. Other examples include U.S. Pat. No. 5,680,321 (determining physical properties selected from dry tensile strength, hydrophobicity, debonding energy, bursting strength, wettability and printability in paper), and U.S. Pat. No. 5,680,320 (quantifying the amounts of reacted and/or retained chemical additives in paper by analysis of the visible, near-infrared and/or infrared spectrum of the paper/pulp in a process line).
While the foregoing art discloses the use of chemometric evaluation in the analysis of paper products, the mechanical properties of wet-solid-wood samples are much more complex due, in part, to the presence of high concentrations of hemicellulose and lignin in wood relative to these components in paper. The structure and macromolecular morphology of wood, such as roughness, color, and orientation also affect the spectral properties of solid wood. For a wet wood sample, the analysis of these properties are is problematic because moisture in the samples, along with the high concentrations of lignin and hemicellulose tends to block or conceal the spectrometric derived information. Furthermore, many of these paper properties are a direct result of the presence of a small amount of an additive, or size or wet-strength resin, rather than a function of the inherent properties of paper fibers.
One example of the characterization of wood is described in U.S. Pat. No. 5,965,888, in which, NIR spectrometric data are obtained from dried wood chips. The method for the determination of parameters of wood panels comprises analyzing the raw wood chips/panels at a moisture content less than 10% by a spectrometric method to provide spectral data, and comparing the spectral data with reference spectral data from a reference chip/panel calibrated to known parameters of panels produced from the reference material, or of the reference panel by multivariate analysis. This method is useful in predicting the quality of a dry wood panel based on an analysis of dried wood chips which are used as a feedstock in the manufacturing process.
NIR has also been used for determination of surface roughness and fiber angle of dry wood relative to the duration of the incident light, and for the evaluation of density and the strength of wood from a dry sample. See, e.g., Hoffmeyer, P., et al., Holz als Roh-und Werkstoff 53 (1995) 165-170 (density and strength from a dry sample).
In both U.S. Pat. No. 5,965,888 and Hoffmeyer, P., et al., Holz als Roh-und Werkstoff 53 (1995) 165-170, reference is explicitly made to the problems associated with measuring the NIR properties of wet wood, and seek to overcome them with use of a dry sample for analysis.
However, none of the foregoing references enables prediction of the dry mechanical strength of wet woody biomass, wood fibers, and various composite materials through the use of VIS-NIR measurements of wet wood coupled with a multivariate statistical calibration model. The multivariate statistical calibration model is obtained measuring the modulus of elasticity (MOE) or modulus of rupture (MOR) of the known dry wood and regressing these values against the VIS-NIR spectrum of the wet wood using multivariate techniques. The VIS-NIR spectrum of an unknown wet wood sample can then be input into the calibration model and be used to predict the strength of that piece of wood when it is dried.
A need therefore exists to ascertain any advantages of VIS-NIR spectral sensitivity to simultaneously measure density, moisture content, slope in grain, microfibril angle, and other wood features, which when coupled with multivariate statistical analysis, will correlate the subtle spectral differences between wet wood samples to predict dry wood mechanical properties, such as ultimate bending strength or MOR and MOE.
One object of the present invention is to provide a method to predict the mechanical strength of dry wood from a wet wood VIS-NIR spectra in a calibration model using multivariate analysis.
Another object of the present invention is to provide a method which is useful in a manufacturing process, for quality control and process monitoring of a feedstock, or product, based on the mechanical properties of dry wood.
A further object of the present invention is to provide a rapid, accurate method for predicting the mechanical properties of standing trees, which is useful in assessing the value of a stand of timber, by quantitatively measuring the quality of the timber.
A still further object of the present invention is to provide a method, which is useful in making timber thinning and harvesting decisions.
An additional object of the present invention is to provide an apparatus for determining the dry mechanical strength of green wood.
The present invention overcomes the problems of the prior art methods by providing a method for predicting the dry mechanical strength for a green wood, comprising: illuminating a surface of the wood to be predicted, the wood having a green moisture content; analyzing the wood surface using a spectrometric method, the method generating a first spectral data; and using a multivariate analysis to predict the dry mechanical strength by comparing the first spectral data with a calibration model, the calibration model comprising a second spectrometric method spectral data obtained from a reference wood, the second spectral data correlated with a mechanical strength analytical result obtained from a reference wood having a dry moisture content.